1. Field of the Invention
The present invention relates in general to electrochemical cells, and more particularly, to a process for conditioning an electrochemical cell in the absence of an additive or an electrolyte co-solvent.
2. Background Art
Conventional electrochemical cells are conditioned, prior to normal use, by cycling (i.e. charging and discharging) the electrochemical cell several times in a controlled fashion. During conditioning of the of the electrochemical cell, a solid electrolyte interface (SEI) or passivation layer is formed. The formation of the passivation layer occurs when an electrolyte component, such as an additive or a co-solvent undergoes one or more chemical changes including reduction or decomposition. Once a stable passivation layer has been formed the electrochemical cell can be cycled, or put into normal operation, in a safe and reliable manner.
While the formation of a passivation layer serves a valuable purpose during operation of an electrochemical, the conventional processes used to form such a passivation layer are not without drawbacks. First, the cost of using conventional additives and/or co-solvents can be expensive, thereby increasing the overall cost of manufacturing the cell. Moreover, incorporating an additive or co-solvent into a conventional electrolyte can, over time, adversely affect the electrochemical performance of the cell. In particular, the additives and/or co-solvents tend to decompose and contaminate the electrolyte, thereby leading to inefficiencies in the cycling process of the electrochemical cell.
It is therefore an object of the present invention to provide a process for conditioning an electrochemical cell that remedies the aforementioned complications and/or detriments associated with conventional conditioning techniques.
The present invention is directed to a process for conditioning an electrochemical cell comprising the steps of: (a) fabricating an electrochemical cell comprising a first electrode which a comprises carbonaceous active material and a lithium polysilicate binder, a second electrode, and an electrolyte, and (b) controllably cycling the electrochemical cell, and in turn, forming a passivation layer near the interface between the first electrode and the electrolyte.
In a preferred embodiment of the process, the step of controllably cycling the electrochemical cell comprises the step of charging and discharging the cell at a rate ranging from approximately 0.01 mV/s to approximately 1 mV/s.
In another preferred embodiment of the process, the step of controllably cycling the electrochemical cell comprises the step of applying and removing an electrical potential difference ranging from between approximately 0 volts to approximately 3 volts.
It is also contemplated that the invention further comprise the step of increasing the coulombic efficiently of the electrochemical cell relative to an electrochemical cell cycled at faster cycling rates.
Preferably the step of fabricating the electrochemical cell includes the step formulating an electrolyte comprising a salt dissolved in propylene carbonate.
In addition, the step of fabricating the electrochemical cell may include the step of formulating a first electrode comprising graphite and lithium polysilicate binder, and a second electrode comprising a lithium source.